1. Field of the Invention
This invention relates to an oven for gas chromatography. In particular, this invention relates to a temperature controlled oven chamber for gas chromatography, whereby the chamber is made of heat insulating walls and contains stationary analytical devices such as a chromatographic column, an air circulating device and a heating device for keeping said column at a desired temperature.
2. Description of the Prior Art
It is known that the analytical devices of a gas chromatograph, such as separation columns, column switching devices, injectors or parts thereof, detectors and change-over valves, have to be maintained at temperatures which are critically constant. For this purpose, particularly the separating columns, but also other parts are disposed in a heat insulating chamber the interior of which is maintained at a predetermined temperature by means of controllable heating and air circulating devices.
In gas chromatography, especially in laboratories, the separating columns have to be changed frequently. Therefore, a good accessibility of the analytical devices is mandatory, particularly when sensitive glass capillary columns and assemblies of interconnected separation columns are used.
It is for this reason that a known version of temperature controlled oven chambers is designed like a warming cabinet having a hinged side panel which can be opened to expose the interior. The stationary analytical devices along with their electric and pneumatic connections are arranged in the interior of the cabinet, and they can easily be connected to external systems, for instance to a mass spectrometer which is to be coupled at the outlet side of the gas chromatograph. A disadvantage of this oven chamber is its poor accessibility through the hinged opening. In addition, there is a hazard of burning for the operating personnel when changes of analytical devices shall be made after an antecedant operation.
In order to improve the accessibility, in another version of temperature controlled oven chambers, the analytical devices are arranged in or on the chamber top which is guided by a column and which can be lifted upward away from the oven chamber or housing. When the chamber top is lifted, the analytical devices are well accessible and there is no danger of burning. However, the electrical and pneumatical connection and supply lines must be flexible and adequately long. This reduces the possibility for coupling with external systems which require short and heated connection lines. Another disadvantage of such a design resides in the fact that a misadjustment of sensitive measuring systems may occur due to a movement of the analytical devices.
The German Auslegeschrift No. 1,181,448 discloses an oven for gas chromatography which has an open and a closed operational position. The oven has the shape of a cylindrical pot. In the closed position, the pot which contains an electric heater is turned upside down over the chromatographic column. The internal temperature of the oven is controlled in order to achieve a value which is of advantage with regard to the chromatographic separation of the substance under examination. A fan which is driven by an electric motor circulates the air inside the pot. After an analysis of the substance under examination has taken place, the pot can be moved upward. In one version of the known oven (see FIG. 1), the pot can completely be removed from the chromatographic column. In this open position, the operator of the oven has free access to the chromatographic column. In this position, the column can cool down quickly, and the column can easily be exchanged. Yet, the known oven has to be disassembled when access to the interior of the oven chamber is necessary or desired. This is a certain disadvantage, in particular since the cylindric pot contains the heater which has to be handled particularly carefully. The hot top part of the oven has to be laid down somewhere, so that some space for this purpose is required. In addition, there is a certain hazard that the column is inadvertantly touched or even damaged when the protecting top part of the oven is removed.